1. Field of the Invention
The invention relates to a recording technique, more particularly to a recording technique for a parity-check-code decoder.
2. Description of the Related Art
Low-density parity-check (LDPC) code is an error correction code. Since LDPC code allows data transmission rates approaching the Shannon Limit, use of LDPC code is increasingly incorporated in communications standards such as Digital Video Broadcast-Satellite Version 2 (DVB-S2), Digital Terrestrial Multimedia Broadcasting (DTMB), and IEEE 802.11. At a signal-receiving end, a LDPC code decoder receives through a channel (N) bits that are to be decoded, and treats each of the bits as a bit node. In order to decode correctly the (N) bits, the (N) bit nodes must satisfy (N−K) conditions, wherein the conditions are called check nodes. Assuming that the check nodes are zeroes, the LDPC code decoder uses the bit nodes and the check nodes to exchange iteratively probabilities of the bit nodes being ‘0’ or ‘1’.
Many LDPC code decoders use log-likelihood ratio (LLR), in which the probability of the bit node being ‘0’ is divided by the probability of the bit node being ‘1’, to represent reliability. As the number of iterations increases, the probability of the bit node being a specific value (that is, ‘1’ or ‘0’) becomes higher, and thereby an absolute value of the reliability value increases accordingly. In an actual circuit, however, only a limited bit length can be used for recording the reliability value. Consequently, the issue remains as to how to record large reliability values. In PROC Patent Application Number 200610012000.9, there is disclosed a method of recording reliability according to the number of iterations. However, since the number of iterations is predetermined, the method may not be suited to actual operating conditions.